This application claims priority to Japanese Patent Application JP 2001-306438, and the disclosure of that application is incorporated herein by reference to the extent permitted by law.
1. Field of the Invention
The present invention relates to a technology for modulating an image displayed on a display screen so as to generate an optical state variation that becomes visible in a recorded image obtained through unauthorized image-capturing of the displayed image and hampers watching of the recorded image.
2. Description of the Related Art
A technology for preventing unauthorized recording of an image displayed on a display screen (image/video piracy) is disclosed in U.S. Pat. No. 6,018,374. In the related art disclosed in U.S. Pat. No. 6,018,374, difference of imaging characteristics between human vision and an image-capturing apparatus such as camera is considered, and infrared light is utilized as a means for preventing image/video piracy. Specifically, the related art employs a system in which infrared light projector is placed in a vicinity of an image projector or any other position far from the screen. In the system, infrared light is projected from infrared light projector to the screen so that infrared light reflected at the screen can fall upon the image-capturing apparatus operated by a person conducting image/video piracy. In other words, the technology enables to record an infrared image unrelated to a feature film/video program image when image/video piracy is conducted. Accordingly, quality of the recorded image obtained through image/video piracy can be damaged, and even a location at which image/video piracy has been conducted may be identified. Of course, audience/spectator/viewer (referred as audience hereafter) directly watching a feature film/video image can enjoy it without any difficulty since infrared light can not be perceived by the human vision.
As described above, sufficient prevention and hampering effect may be accomplished by utilizing infrared light. However, it is desirable to establish a variety of prevention and/or hampering technologies for protecting valuable image/video contents.
According to the present invention, there is provided a technology for applying a periodic modulation to an optical state of visible light that is superposed on an original display image so that, without hampering the direct watching of a displayed image, an optical state variation independent of the original display image can be perceived in a recorded image obtained by image-capturing of the displayed image using a image-capturing apparatus. That is, the modulation technology of the present invention is provided to generate hampering noise (the optical state variation independent from the original display image) that becomes visible when the recorded image is watched and becomes invisible or almost invisible when the displayed image is directly watched.
The optical state variation may include a variation in light-and-dark contrast domain (luminance variation), a variation in color domain, and/or a combination of these variations. In the following section of the present specification, conditions enabling such an optical state variation and application examples utilizing the above-mentioned modulation technology will be described.